Conventional extendible scissors trusses are made up of a number of truss members pivotally joined at their points of crossing to define generally quadrilateral shaped truss cells. Commonly, these trusses are made up of two sets of parallel members which form one or more parallel sided or diamond-shaped cells when the truss is extended. Generally, all of the truss members of at least one of the truss member sets will rotate in a common plane during extension of the truss. Conventional extendible scissors trusses of this nature are used as columns or beams in collapsible structures, to maintain elements of mechanisms in a parallel relationship while allowing the distance between them to be varied, and to serve as collapsible fences or barriers.
An example of the use of these trusses as barriers is the familiar child gate extended across the head of a staircase to prevent children from falling down stairways. Such child gates can be collapsed to one side against a supporting post or wall and selectively extended to provide a guard barrier. Examples of extendible scissors trusses used to maintain elements of mechanisms in a parallel but extendible relationship are found in camera bellows, wherein an extendible scissors truss maintains a lens assembly in parallel relation to a film plane in the camera body when the camera is opened and the lens assembly extended, and in mechanisms by which a platform, such as a truck body, is elevated above its supporting structure. Use of extendible scissors trusses as beams in collapsible structures may be observed in portable stage structures where the extendible scissors trusses are employed between supporting legs or columns to maintain them in vertical parallel relationship and, in some instances, to carry vertical loads from the platform to the legs or columns. An example of collapsible structures utilizing extendible scissors trusses as structural members may be found in my U.S. Pat. No. 4,641,676 which discloses a collapsible canopy structure including extendible scissor truss assemblies.
While conventional extendible scissors trusses have great strength and may be very stiff in resisting loads resulting from forces in the plane of their truss cells and the related moments normal to those cells, they are generally weak and relatively flexible when subjected to side loads imposed by forces acting normal to the plane of the truss cells and the related moments lying in the planes of the cells. The lack of stiffness of conventional extendible scissors trusses not only limits their ability to carry loads normal to the planes of the truss cells, but also reduces the longitudinal or column load which prior art scissors trusses can safely accommodate without danger of structural failure due to buckling of the truss.